Zooplankton biomass, ETS activity and direct measurements of respiration were compared in a study of the Catalan Sea during the summer stratification period, in and around the deep chlorophyll maximum. The pattern of vertical distribution of zooplankton biomass differed from that found on previous cruises, but some trends in the horizontal were similar (minimum inteprated values coinciding with ascending deep waters). Over the Catalan shelf the ETS activity averaged 0.09 µeq h-1.l-1 .The potential respiration, stoichiometrically calculated from the ETS activity, is 0.5 µlO2 h-1.l-1. Seaward of the frontal system on the shelf the rates decreased 50 % and then increased to 0.5 µlO2 h-1.l-1 on the eastern side of the divergence that occurs in the middle of the Catalan Sea. The zooplankton ETS activity did not increase in the chlorophyll maximum. A comparison of the ETS activity in the net and bottle samples suggests a difference in the capture efficiencies by both sampling methods. Physiological measurements of respiration were made on board and compared with ETS activity. A wide range of respiration/ETS ratio (1.60-3.38) was found; the correlation coefficient of respiration on ETS activity was 0.64.